Where is a 15yo not allowed?

We're transplants who moved here last year. We're raising a 15yo. Where we come from, it's pretty clear which places that serve alcohol require you to be 18 or 21 to enter. Almost anyplace that bills itself as a pub or a brewery or has a large bar area doesn't allow minors, even for a meal. Can you help me understand the rules here? Would there definitely be signage on the door letting you know? Thank you!